1. Field of the Invention
The present invention generally relates to a commutator for electric motors and a method for manufacturing the same. More particularly, the present invention relates to a commutator for electric motors of which commutator pieces constituting the commutator are fixed to an insulating material so as not to separate or scatter therefrom during motor rotation and a manufacturing method for the same.
2. Description of Related Art
In a conventional Commutator for electric motors, a cylindrical insulating resin material for electric insulation is filled into a cylindrical conductive material, and a plurality of commutator pieces are formed by forming a plurality of slits on the conductive material in the axial direction thereof to constitute a commutator for electric motors. Furthermore, a latch pin or hook pin is integrally formed at an axial side end of each commutator piece to latch an exciting winding to be wound around a rotor.
It should be noted, however, that commutator pieces of the commutator are subjected to various forces. That is, when an electric motor runs, the commutator also rotates with the rotor, and consequently the commutator pieces constituting the commutator are subjected to centrifugal force. Furthermore, as brushes slidingly contact the commutator pieces, the commutator pieces are subjected to force in the circumferential direction as well. In addition, as the exciting winding is latched on the latch pins, the commutator pieces are subjected to tensile force in the axial direction.
Various structures have been proposed so that the commutator pieces are protected from separation and scatter by those forces, as illustrated in FIGS. 19 through 24.
A commutator 100 illustrated in FIGS. 19 and 20 is composed of a plurality of commutator pieces 102 which are separated from each other by a plurality of slits 101. A pair of folded claws 103 are integrally formed on the axial side ends of the commutator piece 102 respectively, and these folded claws 103 are embedded in an insulating resin material 104.
A commutator 100 illustrated in FIGS. 21 and 22 is also composed of a plurality of commutator pieces 102 which are separated by a plurality of slits 101. A pair of raised claws 105 are formed at the axial side end parts of the inner periphery of the commutator piece 102, and these raised claws 105 are embedded in an insulating resin material 104.
A commutator 100 illustrated in FIGS. 23 and 24 is also composed of a plurality of commutator pieces 102 which are separated by a plurality of slits 101. A plurality of pairs of engagement claws 106 are formed on the inner periphery of each commutator piece 102 at the specified intervals. These engagement claws 106 are embedded in the insulating resin material 104.
However, as the folded claws 103 are made of a sheet of conductive material which is punched and then folded on a press, there is a problem that the yield rate or percentage of use of the conductive material is low. There is another problem that the folded claws 103 may be deformed or broken due to resin forming pressure in the filling of the insulating resin material 104. There is also another problem that, although the commutator piece 102 formed with the folded claws 103 can withstand the tensile force of the exciting winding, it is vulnerable to force in the circumferential direction and centrifugal force.
There is a problem with the commutator 100 illustrated in FIGS. 21 and 22 that the raised claws 105 of the commutator piece 102 may be deformed or broken due to resin forming pressure in the filling of the insulating resin material 104. There is another problem that, although the commutator piece 102 formed with the raised claws 105 can withstand the tensile force of the exciting winding, it is also vulnerable to force in the circumferential direction and centrifugal force.
The commutator 100 illustrated in FIGS. 23 and 24 has a problem that, although each commutator piece 102 can withstand the tensile force of the exciting winding, it is also vulnerable to force in the circumferential direction and centrifugal force. There is another problem that, as the engagement claws 106 of the commutator piece 102 are made by rolling a sheet of conductive material into a cylindrical shape and then forming the slits 101 to divide the conductive material into the commutator pieces 102, a rolling process is required for rolling the conductive material and equipment for this rolling process is additionally required, which requires additional production facility costs.